1. Field of the Invention
This invention relates to a stepless speed change device arranged on a crankshaft of a bicycle and more particularly to a speed change operating and reverse input allowing device for the stepless speed change device of a bicycle, in order to avoid a self-rocking of the mechanism when a crank gear is subjected to a reverse input.
2. Description of the Prior Art
Such a stepless speed change device for a bicycle has been known for example by Japanese Laid-open Patent Application No. 54-93,754, which is provided on a rear hub spindle of a bicycle.
With a bicycle, in general, a diameter of a crank gear is much larger than that of a rear hub sprocket because the rotation of the crankshaft is increasingly transmitted to a rear wheel. When such a speed change device is provided on the rear hub spindle of the bicycle, a diameter of the rear hub sprocket becomes somewhat larger and hence a diameter of a crank gear becomes larger, so that the transmission device becomes larger.
Moreover, such a transmission device generally uses a planetary gear assembly to increase its transmission speed. This increased transmission ratio is determined by a ratio of a diameter of planetary gears to a diameter of a sun gear and pulsations become small with an increase in the number of planetary gears used.
In the event that all the planetary gears and the sun gear are arranged in a plane as in the above stepless speed change device, if the number of the planetary gears P is increased, a diameter of the sun gear S becomes larger to make small the speed-up transmission ratio, while if diameters of the planetary gears P are made larger in comparison with that of the sun gear S so as to make larger the speed-up transmission ratio, the number of planetary gears P becomes less to make large the pulsations as shown in FIGS. 1a-1c.